The Stressor Identification Process
Feb 04, 2016
The Stressor Identification Process
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Define the Case
List Candidate Causes
Evaluate Data from the Case
Evaluate Data from Elsewhere
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
The causal analysis framework
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Define the Case
List Candidate Causes
Evaluate Data from the Case
Evaluate Data from Elsewhere
Identify Probable Cause
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Detect or suspect biological impairment
• Fish kills• Organismal anomalies• Changes in community
structure• Low biotic index values• Violation of biocriteria
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• ‘98 303(d) List
• Public-Owned Treatment Works (POTW) main focus
• TMDLs target Cu, Pb, Zn
POTW
Willimantic River case study#
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POTW
Willimantic River case study#
MR3
MR1
• Impaired site MR3 (↓ EPT taxa)
• Less impaired site (MR1) upstream of MR3
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Triggering the causal analysis
Invertebrate Index Scores as % of reference site RB1
0
20
40
60
80
100
RB1 FB2 FB5 MR1 MR2 MR3 WL1 WL2 WL3 WL4 SR HR TR
moderately impaired
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Step 1: Define the Case
List Candidate Causes
Evaluate Data from the Case
Evaluate Data from Elsewhere
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
• What biological effects are observed?
• Where are they occurring?• Where are comparable
reference sites?
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Example: defining the biological impairment in the Willimantic case study
Biological effect
MR1 (reference)
MR3 (impaired) Change
Number of EPT taxa 17 9 decrease
Making the impairment specificThe more specific you can make—or the more narrowly you can define—the impairment, the better.
•Specific = better discrimination across candidate causes
•Can consider multiple impairments
Level of specificity Examples Utility in SI
LOW Failure to meet biocriteria Triggers SI
↓ sensitive taxa↓ EPT richness
Listing candidate causesDeveloping conceptual model
HIGH ↓ ParaleptophlebiaAbsence of brook trout
Grouping sitesDiagnosing causesEvaluating strength of evidence
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Define the Case
Evaluate Data from the Case
Evaluate Data from Elsewhere
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Step 2: List Candidate Causes
• Make a map• Gather information on
potential sources, stressors, & exposures
• Develop a conceptual model
• Engage stakeholders
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• Focus on stressor(s) that may be causing biological impairment
• May have causal scenarios, with several stressors acting in combination
• Candidate causes may include:–Mechanisms or modes of action–Sources
Listing candidate causes
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MR3
MR1
POTW
Stafford Springs
woodsindustrial
facility farms
Example: the Willimantic River case study
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↑ other toxics
Example: using models for communication
↓ dissolved oxygen
↑ temperature
↓ EPT richness
POTWindustrial facility dams subdivisiondairy farm
↑ NH3↑ Zn
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↑ other toxics
Example: using models for communication
↓ dissolved oxygen
↑ temperature
↓ EPT richness
POTWindustrial facility dams subdivisiondairy farm
↑ NH3↑ Metals
Evidence?
Evidence?
Evidence?
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Define the Case
List Candidate Causes
Evaluate Data from Elsewhere
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Step 3: Evaluate Data from the Case
EVIDENCE FROM THE CASE• Co-occurrence• Exposure or mechanism• Causal pathway• Stressor-response
relationships from field• Manipulation• Lab tests of site media• Temporal sequence• Verified predictions• Symptoms
Supports
Weakens
Spatial/Temporal Co-Occurrence Upstream Downstream Comparison
Physical Interaction
Causal agents change an affected agent by physical interaction.
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Spatial/Temporal Co-Occurrence
Adverse change compared to references
1. Toxics
Upstream reference
Watershed reference
Impaired site
Upstream Watershed
Al 0.080 0.037 0.101 Yes Yes
a 8/28/00b 7/23/01
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Spatial/Temporal Co-Occurrence
Candidate Cause
Measurement Upstream reference
Watershed reference
Impaired site
Adverse change compared to references
1. Toxics
Total Metals and Ammonia (mg/L)
MR1 RB1 MR3 MR1 RB1
Al 0.080 0.037 0.101 Yes Yes
Cd 0 0 0 No No
Cr 0 0 0.005 Yes Yes
Cu 0.004 0.004 0.005 Yes Yes
Fe 0.395 0.208 0.695 Yes Yes
Ni 0 0.001 0 No No
Pb 0.001 0 0.001 No Yes
Zn 0.006 0.004 0.011 Yes Yes
NH3 0.1 0.1 0.1 No No
a 8/28/00b 7/23/01
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Spatial/Temporal Co-OccurrenceSpatial co-occurrence
Candidate Cause MeasurementUpstream reference
Watershed reference
Impaired site
Advance change compared to references
2: High FlowNo Evidence
MR1 RB1 MR3 MR1 RB1
3: Embeddedness% Silt Covered
Substrate0-25% 0-25% 50-75% Yes Yes
4: Low Dissolved Oxygen
Minimum Dissolved
Oxygen (mg/L)
7.32b 10.17b 8.91b No Yes
5: Temperature Stress
Maximum Temperature
22.56oCb 17.28oCa 23.41oCb Yes Yes
6: Altered food resource
No Measurements
a 8/28/00b 7/23/01
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Loss of suitable habitat
Increased amount of
fine particles
Fine particles fill interstitial
spaces
Impoundment
Increased algae
Road Sanding
Loss of invertebrates
Bank Failure
Decreased inter-gravel dissolved
oxygen
Particle settling
Impoundment filling and
particle export
More EPT taxa atMR2 downstream from dam andupstream from MR3
Proportion of substrate composed of sand was half the amount observed at the upstream reference site
Bank stability score was unchanged from upstream; stream banks armored by riprap and granite walls
X X X
Sequential Dependence
All effects result of a prior sequence of cause effect events
loss of interstitial habitat due to settled particles
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Define the Case
List Candidate Causes
Evaluate Data from the Case
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Step 4: Evaluate Data from Elsewhere
EVIDENCE FROM ELSEWHERE• Stressor-response
relationships (from lab, other field studies, or ecosystem models)
• Mechanistically plausible cause
• Manipulation at other sites• Analogous stressors
Stressor-Response Relationships from Laboratory Studies
Weakens Strengthens
Sufficiency The intensity or frequency of a cause is adequate to produce the observed magnitude of effect.
Supports
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Stressor-Response Relationships from Laboratory Studies
CT Values
(ug/L)
Daphnids (ug/L) Test EC20 MR1 Exceeded at
MR1
MR3 Exceeded at
MR3
Al None1 1900 540 82.2 No 107 No
Cd 0.62 0.15 0.75 0.4 Yes 0.5 Yes
Cr 100 <44 0.5 0.2 No 2 Yes
Cu 4.8 0.23 0.205 2.2 Yes 2.5 Yes
Fe None1 4380 - 522.8 No 532 No
Ni 88 <5 45 0.2 No 0.3 No
Pb 1.2 12.3 - 0 No 0.8 No
Zn 58.2 46.73 - 6.5 No 8.6 No
NH3 1430-2470 630 120 No 100 No
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•Impairment is so great, exposure to some agent at highly adverse levels must be occurring.
•Natural variability could not account for this.
Effect Impaired site
Number of EPT Taxa 9
Lacking Sufficiency from Analogous Situations
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Prediction from Analogous Situations
Experience suggests that highly toxic exposures are involved.
1. Bracket site, look for origination of impairment.
2. At the origination, there should be a point source, not non-point source.
3. The point source will intermittently release a highly toxic pollutant or precursor.
Effect Impaired site
Number of EPT Taxa 9
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Verified Predictions of Source
Illicit discharge observed upstream from impairment
Sequential Dependence
All effects result of a prior sequence of cause effect events
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Manipulation of Source/Exposure
SUPPORTSImpairment occurs when stressor present and does not occur when stressor is removed
WEAKENSImpairment occurs when stressor present and when stressor is removed
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0
5
10
15
MR2 MR3 WL1
1999-2000
2001-2002
Mean number of EPT taxa before (1999-2000) & after (2001-2002) rerouting of illicit discharge
Sequential Dependence
All effects result of a prior sequence of cause effect events
Manipulation of Source/Exposure
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Define the Case
List Candidate Causes
Evaluate Data from the Case
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Step 5: Identify Probable Cause
Evaluate Data from Elsewhere• Weigh strength of
evidence for each cause– eliminate if you can– diagnose if you can
• Compare strength of evidence across causes
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Willimantic case studyMetals NH3 Flow Silt Low
DOTemp Food Episodic
Mix
Types of Evidence that Use Data from the Case
Spatial/Temporal Co-Occurrence + - + - - - + +
Evidence of Biological Mechanism + + + - + + - +
Causal Pathway - + - - + - +
Stressor-Response from the Field + - - + +
Manipulation + + +
Verified Predictions + + +
Types of Evidence that Use Data from ElsewhereStressor-Response from Other Field - - +
Stressor-Response from Laboratory + + - - +
Example: strength of evidence analysis
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How to evaluate consistency of evidence
Candidate cause
Type of evidence NH3 Cu TSS
Co-occurrence + – +
Causal pathway + – –
Manipulation + – +
Stressor-response + – –
CONSISTENCY supports weakens weakens
Willimantic case study Metals NH3 Flow Silt Low DO Temp Food Episodic
Mix
Types of Evidence that Use Data from the Case
Spatial/Temporal Co-Occurrence + - + - - - + +
Evidence of Biological Mechanism + + + - + + - +Causal Pathway - + - - + - +Stressor-Response from the Field + - - + +Manipulation of Co-occurrence + + +Verified Predictions + + +
Types of Evidence that Use Data from Elsewhere
Stressor-Response from Other Field - - +Stressor-Response from Laboratory + + - - +
Evaluating Multiple Types of Evidence
Consistency of Evidence - - - - - + - + + +
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↑ other toxics
Example: using models for communication
↓ dissolved oxygen
↑ temperature
↓ EPT richness
POTW dams subdivisiondairy farm
↑ NH3↑ Cd
DO higher at impaired site vs. reference
industrial facility
after rerouting industrial discharge had decreased concentrations of Zn & other toxics, increased EPT taxa richness
NH3 same at impaired site and references.
Cd greater at impaired site vs. reference, but not at levels sufficient to cause impairment
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Define the Case
List Candidate Causes
Evaluate Data from the Case
Evaluate Data from Elsewhere
Identify Probable Cause
Detect or Suspect Biological Impairment
As Necessary: Acquire Data
and Iterate Process
Identify and Apportion Sources
Management Action: Eliminate or Control Sources, Monitor Results
Biological Condition Restored or Protected
Decision-maker and
Stakeholder Involvement
Stressor Identification
Causal analysis is one step in management process…
• After causes are identified, sources & management actions must be identified
• Biological monitoring verifies that actions are effective
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